Embankment on muskeg and associated methods

ABSTRACT

Described are techniques for building improved roads and embankments on muskeg terrain; with an embodiment for a timber haul road using a substrate mat of rigid polyurethane form supporting a properly-distributed embankment of native gravel (or like road building material), preferably distributed in a &#39;&#39;&#39;&#39;counterbalancing berm&#39;&#39;&#39;&#39; construction and providing an improved stable roadway embankment in the face of stress conditions typical of muskeg areas.

United States Patent 1191 Burt et al. Apr. 29, 1975 [5 1 EMBANKMENT ONML'SKEG AND 2.211.649 8/1940 Drury 404/28 ASSOCATED METHODS 2.737.0923/1956 Gramezspacher 404/28 3.022.712 2/1962 Cousino 404/17 X 1lflvemorsl Glenn Bllrl, Deer k TeX; 3.474.625 10/1969 Draper 404/17 xRichard L- odsa her. F irb nk 3.626.702 12/1971 Monahan 404/28 x Al askaOTHER PUBLICATIONS Asslgnee! Atlantic Richfield p y- Dow ChemicalCompany, Publication Form No.

New York- NY l7l-300-3M-9/64.

[22] Fllcd: I974 Primary Examiner-Nile C. Byers, Jr. [2]] App]. No.:441,095

Related U.S. Application Data 57 ABSTRACT FS IL of 258457 May 1972Described are techniques for building improved roads and embankments onmuskeg terrain; with an embodiment for a timber haul road using asubstrate mat of [52] U.S. Cl 404/28; 404/82 I rigid polyurethane formsupporting a properly- [51] Int. Cl. E0lc 3/00 distributed embankment ofnative grave] (or like road [58] Field of Search 404/ 8 7 17 71 31building material), preferably distributed in a counterbalancing berm"construction and providing an im- [56] References cued proved stableroadway embankment in the face of UNITED STATES PATENTS stressconditions typical of muskeg areas. 584.083 6/1897 Nichol 404/27 X1.421.901 7/1922 Brotsch 404/27 12 Clams 3 Drawmg Flgures EMBANKMIENT ONMUSKEG AND ASSOCIATED METHODS This is a streamline continuation, ofapplication Ser. No. 258,457 filed May 31, 1972, and now abandoned.

BACKGROUND, PROBLEMS, PRIOR SOLUTIONS Muskeg is typical of highlyorganic soils characterized by a low unit weight, low shear strength,high moisture content, high porosity, and high compressibility.Obviously, muskeg is not generally considered in any way desirable as asubstrate for road building; however, at times it must be used, forinstance in constructing timber haul roads and other access ways invarious sub- Arctic regions such as parts of Southeastern Alaska andSouthern Canada.

Methods commonly employed for building roads on muskeg are, as yet,relatively crude. They include the excavation method" wherein the muskegmaterial is dug out and replaced by a suitable granular fill of roadwaymaterial, such as native gravel. Another method involvespreconsolidation or artificially containing and pressing the muskeg toreduce void percent. Another is the displacement method (akin tocauseway construction by gravity displacement) wherein fill material iscontinually piled upon muskeg at the site until enough sinks tocompletely displace the underlying muskeg.

Floating" is another method and, in general, in volves simply piling-upgranular fill directly atop the muskeg bed as in normal roadconstruction in a manner which prevents it from sinking (floating theroad). In its crudest form this method is quite inexpensive initiallybut limited in load-bearing capacity and apt to involve costlymaintenance over a period of time. Corduroy, brush, sawdust and/orconsolidated straw (bales or fascine bundles) are frequently used inconjunction with this floating construction to provide buoyancy andweight distribution. Differential settlement problems can generate a topembankment surface which is so uneven as to be utterly useless unlessrepaired (and repairs are apt to be frequent with changing subsurfacehydraulic conditions). Pumping and related problems of liquid intrusioninto the gravel embankment are also common with floated embankments andcan destroy a structures integrity, dissipating the material outward,and requiring frequent repairs with supplemental flll. The presentinvention is directed toward improving such floated" construction.

Further particulars on conventional construction like the foregoing maybe had by reference to the Muskeg Engineering Handbook" (1969) publishedby the National Research Council of Canada. None of the foregoingmethods are fully satisfactory; in many cases, being unnecessarilyexpensive in terms of construction time and costs, and/or requiringextensive maintenance, and/or relatively unsatisfactory in performance.

In considering various solutions to the problem of constructing roadsover muskeg, it occurred that a plastic web such as polyethylene film orsheeting could be employed as a combination moisture-barrier andembankment-containment means. However, such a web must not be readilyruptured since this will result in contaminant intrusion and/or escapeof embankment material, leading to failure of the road section. Asolution, described according to this invention, as indicated in theembodiments below, is to employ a rigid synthetic polymeric foam tofunction as a somewhat resilient substrate mat placed atop the muskegand on which the gravel (or other particulate) roadway material may beproperly distributed to form a floating embankment-rnat structure.Preferably this gravel material is so distributed on the mat so as togenerate a high degree of uniform consolidation in the muskeg under theroadway (load-bearing portion), primarily by producing a prescribedintegral mat-embankment structure (or a monolithic pad) which bears uponthe muskeg substrate so as to effect this. In most cases this will beeffected by the use of the described flanking berm construction wherebythe contemplated roadway track (load bearing portion) is flanked byberms of gravel on both sides acting to counterbalance one another andstabilize the overall embankment. Workers in the art will discern thatsuch improved embankments can readily result in major reductions in thecost and associated problems of building and maintaining roads on muskegand offer significant cost/benefit factors. Further advantages anddistinctions of the invention will become more apparent uponconsideration of the following disclosure in conjunction with theaccompanying drawings wherein:

DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 comprise isometric sectionalelevations, in cross-section, of a preferred muskeg road embodiment,with FIG. 1 indicating schematically the general plan whereby thesupporting mat and the various masses of embankment gravel are to bedistributed; while FIG. 2 indicates the contemplated finished conditionof this embodiment, after settlement and other equilibrium conditionshave been reached; and

FIG. 3 indicates an embodiment after the manner of FIG. ll, however,modified to also include a pair of reinforcing track strips.

SUMMARY OF THE INVENTION The present invention contemplates using webmat structures to support particulate embankment construction on muskeg(or similar) terrain, with the form and placement of the mat and theembankment material masses being arranged so as to effect a proper highdegree and uniformity of consolidation at least below (supported)working portions of the roadway.

It will be evident that a primary object of the subject invention is toresolve at least some of the foregoing problems and provide atleast someof the associated features and advantages. A related object is toprovide an improved method of embankment construction for muskegterrain. A further object is to provide such an improved method usingmat construction for supporting embankment material upon the muskegsubstrate. A related object is to so arrange and distribute this matmaterial and the supported embankment (particulate) material as toprovide an integral floating load structure, acting to uniformlycompress the muskeg substrate to a high degree over a fairly extensivearea and thereby stabilize (at least the traffic portions of) theroadway and improve its performance in service. A further object is toprovide such a construction and thereby present a floated embankmenthaving a more stable, uniform load distribution. A related object is toprovide such a construction with a moisture-barrier which is relativelyimpervious to liquid intrusion into the embankment mass. Yet anotherobject is to provide such a structure, using flanking berm" constructionand thereby better stabilize and balance the overall structure upon themuskeg, while reducing shear and rupture stresses upon the mat material,while also acting to spread and better distribute the masses andinertial loads across the embankment (and mat). A further object is toprovide such a structure, as reinforced, at least beneath load-bearingregions, so as to reduce the prevalent rolling wave" phenomenon. How theforegoing and other more specific objects are achieved will becomeevident through consideration of the ensuing description of preferredembodiments of the invention in conjunction with the associateddrawings.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 is a schematic, idealizedcross-sectional indication of one advantageous method of constructing animproved embankment according to the invention. More particularly, FIG.1 indicates the placement and distribution of a supporting mat 2 andembankment gravel material disposed thereon to comprise a particularroadway structure 1 supported upon muskeg terrain (the muskeg groundsurface being indicated schematically at level M; while the water tablelevel is indicated slightly below, at level WT). While FIG. Iparticularly indicates the manner of gravel distribution for roadway land is somewhat idealized, while FIG. 2 comes closer to representing theactual operational form of the embodiment, once all the gravel has beenpiled on in the appropriate manner and, it and the muskeg substrate Mhave settled and become properly consolidated, etc., under the loadingthis presents (l.e., after the system has come to equilibrium). Roadwayembankment 1 will be more particularly understood as an improved haulroad (e.g., for timber) over muskeg, with the embankment material 4comprised of native gravels of typical (e.g., properly graded anddrained) roadway material as commonly used in the art for such areas,thus road 1 is assumed to be relatively conventional in characteristicsand construction except as herein described.

The environment and locale for placement of roadway I will be betterunderstood as comprising a muskeg bed of the type commonly found inSoutheastern Alaska, the muskeg material MUS." comprising about 90percent water with the balance mostly organic matter and having arelatively typical void ratio (understood as about here) andwell-saturated with water below the water table WT, being on the orderof about 6-10 feet above solid footing (GD) (see depth DM in FIG. 2).Other characteristics of the muskeg will be better understood byreference to Table I below.

TABLE I MUSKEG CHARACTERISTICS Water Content 700-l00071 Specific Gravity1.3-1.6 Void Ratio l0-l5 Organic Content -90% Vane Shear Undisturbed 250psi Vane Shear Remoldcd 100 psi Depth of Muskeg 6-l0 ft. to hard bottomin FIG. 2). More particularly, mat 2 preferably comprises a relativelyrigid polyurethane foam in mu tilaminate form, having a compressivestrength on the order of at least 35 psi (at 5 percent deflection) andgenerally having the requisite tensile strength, moistureimperviousness, and other characteristics indicated for the subjectenvironment. Mat 2 must be such as to maintain absolute integralcontinuity without rupture under the strain of supporting both theembankment road 1 and any contemplated loads thereon upon the subjectmuskeg bed without rupture of the passage of liquid or substratecontaminants or embankment material. Further, it must be somewhat rigidand able to maintain the desired configuration (FIG. 2 for example)despite localized differential support variations such as those due tolocalized variations in water content of the muskeg. It must also bestrong enough to resist rupture and piercing by commonly availablehazards such as sharp stones, sticks, and the like. For this purpose, aswill be understood in the art, mat 2 may be provided with reinforcementmeans therein, such as nylon mesh material added as a supplementallayer.

Turning to the particulars of the embankment material comprising roadwayit will be noted that the primary embankment 5 comprises a prescribedmass of native gravel material piled into an embankment of prescribedwidth WR and height H (here understood as about 12 feet wide by about 4feet high assuming granular fill weight of about pounds per cubic footon muskeg MUS, which has about I00 psf shear strength). Embankment 5will have a prescribed travelling surface 11 (or wear surface coveredwith the conventional wear coating if desired and as if conventional notshown or discussed) and sloped shoulders 13,13 for structural stabilityas is conventional in the art.

In addition, roadway embankment 1 preferably also includes a pair offlanking berms 7,7, arranged along the margins of roadway embankment 5and serving to impart a prescribed overall balanced embankment load uponsupporting mat 2 and the muskeg material therebeneath. That is, berms7,7 are comprised of the same native gravel material as embankment 5 andhaving generally speaking, respective height and width dimensions (W-B,W-B' and HB,HB' respectively) generally about one-half the correspondingdimensions of embankment 5, although this will vary somewhat asindicated below. Berms 7,7 will interrupt the ditch of shoulders 13,13with these being continued at their outer margin as indicatedrespectively at shoulders 9,9 which are tapered into the surface of themuskeg bed M, as is conventional. Thus, the overall width W-RW of theentire roadway embankment l is somewhat in excess of twice the roadwaywidth W-R for this embodiment.

It will be seen that the flanking berms function as a counterweight andto extend the gravel-load area upon mat 2 most especially to helpflatten the consolidation pressure profile (stress bulb) at the center,or working portion, of roadway 1. More particularly, as indicated inFIG. 2 with the equilibrium condition of the entire gravel system asindicated leaving a central roadway or traffic strip W-R, the portion ofweb 2 directly below this traffic strip (manely, central web segment2-C, preferably being at least as wide and usually wider than strip W-R)will be so loaded by the overall gravel system as to impart a relativelyhigh, yet uniform, loading pressure upon the bearing zone CA in themuskeg (indicated in FIG. 2). As workers in the art will readilydiscern, the effect will be to load zone CA in the manner of a flatmonolithic extended plate to impart relatively high, yet uniform,pressures upon this zone (preferably doing so on a gradual manner asindicated below) and gradually expel the liquid content of the muskeg inthis zone without, however, dislodging a significant portion of thesolids therein. As a result, zone CA tends to approximate a structuralpillar supporting the (central portion of) embankment 1 upon the solidfooting (ground level GD), thereby supporting and stabilizing the roadso as to support a prescribed traffic loading. (Arrows S are intended toschematically indicate the gradual expulsion and squeezing-out ofliquidfrom zone CA to consolidate and solidify it in the manner indicated). Itwill also be apparent that this mode of loading (i.e., creating the flatcentral segment 2-C of mat 2 and the smooth continuously decreasingloading outwardly thereof) will impart a relatively smooth, continuousconformation to mat 2 and will tend to minimize any sharp angles orconsequent high shear-loading tending to rupture or over-stress the mat.It will further be apparent to those skilled in the art that theconfiguration of each flanking berm will be such as to distribute gravel(height and position) so as to impart the proper, balanced moments aboutthe inertial center of the entire embankment structure. This mode ofconsolidation will distribute the loading stresses outwardly from thecenter of the web in the indicated gradual continuous decreasing manner.It will further be apparent why this flanking berm construction isespecially helpful and advantageous in areas where such shear failure ismore likely (e.g., where the water content of the muskeg is particularlyhigh). Of course, these masses may be differently distributed (dependingupon the density of the native gravel used, as well as its placementfrom the center) where a different final configuration" of mat 2 isdesired. For instance, whereas the mat configuration in FIG. 2. isrelatively convex (viewed from beneath); in certain instances workerswill perceive advantages in making (at least a portion of) the matconcave-downward, expecially at the outer edges (e.g., to impart adownward curl to the outer mat edges and thereby help contain andrestrain the underlying muskeg material, inhibiting its escape outward).In the embankment of FIG. 2, it will be noted that the mat configurationassumes a somewhat bell-shaped (or catenary) form, with a flattenedcentral section (across the traffic bearing portion) so thatcontemplated traffic loads will have little effect upon the load bearingproperties of the overall roadway I and especially will not change thedegree of supporting muskeg consolidation significantly. Thisconsolidation of fines under the roadway of course produces a morestableroadway (the muskeg in zone CA should be pressed or pre-consolidated soas to be relatively firm and unyielding upon application of the expectedtraffic loads). Workers in the art will further observe that theconfiguration of mat 2 in FIG. 2 will be such as to present no sharpdiscontinuities in (tensile) stresses along the cross-section of the matwith the inertial moments imparted by the gravel distribution(arrangement of berms) being such as to optimize this. The proper use ofsuch counterbalancing berm masses can thus produce a flat uniform highdegree of consolidation of muskeg under the working section of theroadway. Workers in the art will note that FIG. 2 shows essentially noraised center berm portion in roadway 1 as settled in equilibriumcondition; this should present no problem as long as some small degreeof free-board above the water line WT is present. (Note below that it isthe inertial masses and not the shapes of the berm and center embankmentthat are most important here).

Regarding the embankment masses, the following may be noted, the fillheight of center primary embankment 5 (height Pl) may typically bevaried from the order of 1 A: to 4 feet, depending upon the recitedproperties of the muskeg encountered. The maximum height that can beplaced initially on mat 2 without likely shear failure, and rupture(assuming mat 2 is constructed as indicated above) will occur at theorder of between 4 and 5 feet (assuming granular fill of about 125 poundper cubic foot density and muskeg shear strength on the order of psf).Of course, as height h is reduced, the masses of berm 7,7 may bereduced, and in certain cases eliminated where they are not needed toprovide the counterbalancing and stability; although in most cases theywill be useful to provide a margin of safety resulting from the widerdistribution of gravel mass and the resulting larger counterbalancingmoments. The advantages of such flanking berms will be apparent toworkers in the art. For instance, they can reduce the need forcompacting the muskeg substratum and can assist in assuring againstshear failure of the mat, even when service conditions (e.g., loading,water level, pumping from outside, etc.) shift. Moreover, this in turnconserves the fill material since it is not lost, wasted or contaminatedwith leaks as in typical prior art structures (e.g., where the granularfill gradually spreads outwardly more and more invading the muskeg bedand reducing the working portions of the embankment). It will beapparent, moreover, that for a given amount of granular fill, the moreexcess fill (that is, fill not directly necessary as the roadwaystructural material, e.g., in embankment 5) is spread laterally awayfrom the center of the roadway, the greater is the degree of stabilityand the more efficient is material usage for structures of the typedescribed. Moreover, the ultimate consolidation (e.g., in muskeg zone CAof FIG. 2) realized by improved embankment construction according to theinvention will produce a higher degree of consolidation than many priorart structures, depending upon the amount and distribution of the loadson the associate mate (the placement and weight of embankment material,service traffic and the like) as well as upon the characteristics of themuskeg (e.g., its void ratio, moisture content, materials make-up,overall depth and dynamic response). It has been found that themagnitude of settlement during service can be expected to depend to agreat degree upon the change in void ratio of the muskeg thisi in turnbeing primarily dependent upon loading. Thus, the configuration of theembankment mass indicated in FIG. 2 is intended to reflect this. Suchfloating-mat embankment structures may be readily distinguished fromcertain apparently similar construction, such as bridging structureswhich comprise a rigid platform or containment structures which isreally floated upon the semiliquid musket body (a floating bridge). Withsuch a floating bridge, the necessary supporting strengths of theunderlying material will need to be so great and the mass of requiredfill material so great as to dictate a structural support member whichare vastly different from web 2 indicated, or the like.

APPLICATION minimum uniform thickness of about three inchescomcompletely cured. This will provide a multi-laminate structure havingsuperior strength and resistance to moisture intrusion. A foam of 1 /2inches in total thickness is applied in successive layers with 4 to 5per inch of foam, so that each layer is separated by a high densitylaminar skin several mils in thickness, the skin being formed byexposure of the upper surface to air for a period which is a function ofthe ambient temperature. At an ambient temperature of about 70F. thisfoam will rise in about 6 seconds and set in about 12 seconds, while thetime for complete curing will range up to minutes or more. Artificialheating catalyst additives or the like can, of course, acceleratecuring.

Properties of the spray-applied polyurethane foam are shown below inTable II.

prising a laminate of about 4 to 5 layers. The foam is allowed to cureand a moisture-sealant Top-coat layer is preferably applied thereafter.After this, the gravel fill may be piled on the so-form'ed foam mat and,settlement allowed to take place, with fill being piled on until arelatively flat, level roadway surface ll-A is rendered.

Mat 2 is preferably fabricated as follows. To the sur-- face of themuskeg bed (substratee) a hydrophobic, or water-impermeable, base(Pre-coat) layer is applied with conventional, manual, hot-sprayequipment, heated so that, after application, the base layer will be atabout 70F. This layer is a liquid bituminous mixture of Prudhoe Bay 70volume percent crude residuum. For cold-flexibility it may also beextended with low molecular weight polymer as described below. Dependingupon the condition of the substrate, the thickness of this base layer isfrom about one to several tenths of an inch. The colder and wetter thesurface, the thicker this base coat. Since it is a hydrophobic material,any minor amount of moisture that may be in evidence upon the muskegsurface should not be sufficient to inhibit subsequent foaming. Underthese conditions the Pre-coat applied warm as has been described, willallow the first foam layer to react fully, foam properly and thusprovided a strong, coherent initial foam laminate.

Thus, after this bituminous base layer has been applied and while it isstill warm, polyurethane foam insulation is applied on its surface withconventional foam spray equipment, such as a Gusmer pneumatic-mix sprayapparatus having a base heater providing a 140F. block temperature and al l5l20F. hose temperature. The polyurethane is obtained from equalparts of a polyether-polyol and a polyisocyanate wherein the polyol hasa Brookfield viscosity of about 250 cps at 70F. and a density of about9.8 pounds per gallon.

The foam components are sprayed-applied, preferably in superimposedlayers (laimnates) wherein each layer is allowed to set (skin forming)but not to become After the uppermost layer of polyurethane foam skinhas fully cured, the top skin is coated with a second hydrophobic (orwater-impermeable) layer. This Topcoat may be the same composition asthe described base layer, but preferably contains a greater proportionof extender (i.e., of the order of up to 25 percent or more), and has athickness of 0.1 inches or more. This will optimize protention of theuppermost foam laminate, not only from moisture penetration but alsofrom mechanical stresses and consequent rupture. With mat 2 sofabricated, it will of course be necessary to protect it mechanicallyfrom traffic loads, abrasion, etc., by covering it with the usual mantleof highway gravel" or the like. For particularly heavy vehiculartraffic, it is advised that such a mat be covered with a minimum ofabout 18 to 24 inches of native graded gravel. This will preventvehicles from damaging the mat, distributing the heavy vehicular loadsover a wider mat area, as is known in the art.

The composition of the hydrophobic (or water impermeable) Pre-coat layeris preferably bituminous as mentioned. Although asphalts, pitches andthe like could be used because of their water-impermeabilitycharacteristics, these could form steam from the wet muskeg and mightrupture the asphalt coating. If applied as cut-backs (i.e., naphtha orsolvent solutions) there would be a fire hazard when the hotpolyurethane reactants were applied. Aqueous emulsions are not desirablesince, as is known, water is very deleterious to the polyurethanereaction. Moreover, the Pre-coat should be sufficiently warm so that theadequate foaming occurs, and quickly.

It has been found that a long crude oil residuum can be used for thebituminous Pre-coat barrier. Thus, for example, the crude oil from theNorth Slope of Alaska may be topped to remove the most volatile part ofthe crude amounting to about 10 volume percent. The topping can be usedas fuel or added to other crude for shipment or transport. The next 20volume percent of the crude is removed for diesel fuel (e.g. trucks,machinery, power generation and the like). The

next 70 volume percent residual fraction boiling above range of thediesel fuel fraction has been found to be particularly suitable as ahydrophobic (or water impermeable) base material for the Pre-coat. Thiscan be used without further treatment. or it can be air blown toincrease its viscosity and oxidized material employed.

It may be preferred, where cold-flexibility is important, to also add asmall amount of polymeric material to the residual fraction in order toprovide the residuum with increased viscosity and better ductility andflexibility at low temperatures. A satisfactory water impermeablePre-coat consists of 85 weight percent of the 70 volume percent Alaskancrude residuum, weight percent of commercial low molecular weightpolyethylene (19,000 number average molecular weight) and 5 weightpercent ofa commercial styrene-butadiene rubber having a Mooneyviscosity (ML-4 at 2l2F.) of l05-l 10. In general, the polyethylene canhave a number average molecular weight in a range of 18,000 to 30.000and the styrene-butadiene rubber can have Mooney viscosities, (ML4 at212F.) of 45-110.

The polymeric material is incorporated into the residuum at atemperature sufficiently high (for example 140F. or higher) that theresiduum is highly fluid; thereafter the warm (50 to 70F.) mixture isapplied to the substrate. The polymer content of the residuumpolymermixture can range conveniently from 5 to weight percent of the mixturewith the amount of polyethylene to styrene-butadiene rubber ranging inweight ratio from 1:1 to 3:l. Although none of these proportions areextremely critical, large deviations from them give less desirablematerials both from the standpoint of cost and also performance.

Since a relatively thin Pre-coat is applied (to mils), the viscosity ofsuch material should not be so high that a uniform coating cannot beattained. When the Pre-coat is applied to wetter substrates it can besomewhat more viscous since thicker coatings are desired, but uniformityis also a desirable object in these applications. If desired, theresidual component may be air blown to increase its viscosity somewhatand thus little or no polymer need be added to give the properviscosity. As stated. some elastomeric polymer will be desirable wherethe Pre-coat should have good low temperature ductility and flexibility.This is also desirable where freezing and heaving of the muskeg surfacemay occur.

Although workers skilled in the art will contemplate other matconstruction modes, the described embodiment of a rigid polyurethanemulti-laminate foam layer is advantageous for many applications. Furtheradvantage will usually be derived by adding one or both of the describedbase and top hydrophobic (or waterimpermeable) protective layers.

In certain instances where reinforcing strips (see strips 3'/3 in FIG. 3for instance, described below) are employed. these strips will be placedafter the initial foam thickness is applied, being properly adheredthereto; e.g., with a conventional adhesive, and the overall structuretoppedwith a final moisture-sealant coating of the type described incopending application entitled Structure for Protecting and InsulatingFrozen Substrates and Method for Producing Such Structures, Ser. No.205.38l. flled Dec. 6, 1971 by by A. C. Condo. G. R. Knight, G. R. Burt,and A. E. Borchert. As a preferred and further improvement of theforegoing structure in FIGS. l and 2, reinforcing means may be appliedto the support mat to strengthen it in the area of maximum stress (e.g.,below the track area indicated schematically as directly below thewheels of vehicle 2 in FIG. 3, where reinforcing strips 3, 3' arelocated). Thus, as indicated in FIG. 3, a pair of polyurethane foamreinforcement strips .3 are provided upon the underlying mat 2 andpositioned so as to generally underly the track area of the contemplatedvehicular traffic. Strips 3, 3 comprise polyurethane rigid about 4inches high by about 18 inches wide. They are preferably prefabricatedand laid upon mat 2 once it has been sufficiently cured, being adheredthereto in any suitable manner. Similarly, compatible reinforcementmaterial such as polystyrene strips or boards or the like may besubstituted for strips 3, 3 as understood in the art. With suchreinforcement means it will be apparent that the normal rolling wavewhich may be expected to precede some forms of vehicular traffic, oversuch a composite web-supported embankment, will be abated and minimized.Without such reinforcement, as the vehicle proceeds along an embankmentlike embankment 1 herein it may build up and be preceded by a standingwave" of granular material along the surface of the roadway 11;especially in the cases of heavier, faster-moving loads.

Workers in the art will appreciate the improved desirable resultsachieved by the foregoing construction and especially the use ofurethane foam web such as those described. For instance, tests haveindicated that the modules of rupture for the described foam is about 60psi (calculated from Bean formula).

Workers in the art will recognize that the novel features of thisdisclosure may be applied, alone or together, in other contexts to solvedifferent but related problems and that the implementation suggested inthe foregoing embodiments may be modified to achieve the describedresults. For instance, where roadways were mentioned primarily in theembodiments, it will nonetheless be apparent that the same kind ofrestoration and construction techniques may be applied for gravelbuilding-pads or other emban'kments in muskeg or the like wet,high-void, soils. Similarly, for the insulating material; while urethanefoam has been suggested in the embodiments, there will be instancesrecognized by those skilled in the art where other equivalent syntheticweb material will serve, such as polystyrene foam, or in certain casesceramic materials or various native structural materials. In particular,where inexpensive insulation is particularly desired, a mat may beformed from a petroleum-extended polymeric foam (extended with theresidue of a crude distillate or the like). In certain instances theincorporation of air or other blowing and- /or oxidizing and thickeningagents will be preferred (e.g., conventional air-blowing techniques), sothat the active hydrogen content of the material be increased similar towhat is done for asphalt coatings in like instances. Likewise, althoughcertain preferred application techniques for the foam, the Pre-coat, andTopcoat have been described, workers in the art will in some instancescontemplate other application and/or fabrication techniques as suitable.

Workers in the art will further appreciate that the soconstructedurethane foam mat 2, having been foamed in place will insure a totallymonolithic structure capable of performing at least two very desirablefunctions; namely, distributing a point load uniformly over a great areaof the underlying muskeg; and acting as an impervious barrier to preventpumping" and eventual contamination of the granular fill by subsurfacemoisture. To perform these two functions the urethane must besufficiently rigid, yet have the ability to eventually conform to theunderlying muskeg substrate conformation. As a further beneficial sideeffect, such a foam mat will also provide a thermal barrier preventingseasonal frost penetration into the subsurface muskeg and any resultant,damaging heaving, etc.

What is claimed is:

l. A method for constructing improved, more stable embankments uponmuskeg-type terrain, such embankments contemplating the imposition ofrelatively high loading on a prescribed bearing portion thereof, themethod comprising the steps of:

a. Placing a continuous, structurally integral waterimpervious matstructure upon the surface of the subject terrain so as to cover anddefine the contemplated embankment site and b. Distributing particulateembankment materials upon this mat structure so as to generate a centerregion of maximum static loading of the mat structure, therebydepressing the mat configuration thereunder and thereby tending touniformly consolidate the underlying muskeg terrain to a high degreesufficient to be relatively rigid and incompressible under thecontemplated surface loading.

2. The method as recited in claim 1 wherein the embankment materials aredistributed according to a flanking berm" mode so as to counterbalancethe said center high loading materials by the weight of embankmentmaterials distributed outward therefrom in a counterbalancing manner.

3. An embankment road constructed of a prescribed particulate materialon terrain comprising a surface layer of light compressible soilmaterial of relatively high water content, this road comprising: asubstrate mat structure placed upon this terrain so as to define thecontemplated road and support said particulate road material; and anarray of said road particulate materials distributed upon said matstructure so as to develop'sufficient static loading on saidcompressible soil material at the center of the roadway to therebyrender it relatively rigid and incompressible under contemplated surfaceloading and thus form an improved highly stable roadway structure; saidmat being formed to comprise a continuous structural-integral layer ofwater-impervious materials while supporting the described loads withoutrupture thereof.

4. The road structure recited in claim 3 wherein said mat is comprisedof relatively rigid polymeric materials.

5. The composition as recited in Eiaim 4 wherein said mat includes rigidstiffener means affixed thereon directly under the maximum-loadedtraffic sections of the road so as to minimize any rolling wavephenomenon.

6. The combination as recited in claim 4 wherein said mat comprises alayer of polyurethane foam material of sufficiently high compressivestrength to support the contemplated loading without rupture and asupplemental reinforcement layer.

7. The combination as recited in claim 6 wherein said polyurethane foamis applied in a multi-laminate form and wherein a precoat ofwater-impervious material is applied prior to application of the foamand said reinforcement layer is nylon mesh material.

8. The combination as recited in claim 7 wherein said precoat iscomprised primarily of bituminous materials extended by a polymericextender adapted for low temperature flexibility of the mat in service.

9. A method of floating an improved more stable gravel road atopmuskeg-type terrain comprising the steps of:

a. Placing a continuously structurally integral polymericwater-impervious mat upon the terrain surface so as to define theroadway site;

b. Distributing particulate materials upon this mat so as to form theroadway embankment in a manner that develops a centraltraffic-supporting region of maximum uniform weight, tending to depressthe portion of the supporting mat thereunder and consolidate thesupporting muskeg materials thereunder.

10. The combination as recited in claim 9 wherein the particulates aredistributed in a flanking berm" mode so as to develop said depressedcentral mat section and maximum central static loading while alsocounterbalancing and stabilizing this and gradually diminishing thestatic loading upward therefrom thereby minimizing any sharpdiscontinuities of stress upon the underlying mat and minimizingresultant shear and a tendency to rupture.

11. The combination as recited in claim 9 wherein rigid reinforcingstiffener means is affixed to the mat structure along portions thereofunderlying the contemplated traffic load, said means being sufficientlyrigid to minimize and rolling wave" phenomenon.

12. The combination as recited in claim 9 wherein said mat is so formedand comprised of materials as to render a monolithic structuredistributing loads over a larger area of supporting terrain and so as tofunction as a barrier, both to the intrusion of moisture and to theescape of particulate roadway materials therefrom.

1. A method for constructing improved, more stable embankments uponmuskeg-type terrain, such embankments contemplating the imposition ofrelatively high loading on a prescribed bearing portion thereof, themethod comprising the steps of: a. Placing a continuous, structurallyintegral water-impervious mat structure upon the surface of the subjectterrain so as to cover and define the contemplated embankment site andb. Distributing particulate embankment materials upon this mat structureso as to generate a center region of maximum static loading of the matstructure, thereby depressing the mat configuration thereunder andthereby tending to uniformly consolidate the underlying muskeg terrainto a high degree sufficient to be relatively rigid and incompressibleunder the contemplated surface loading.
 2. The method as recited inclaim 1 wherein the embankment materials are distributed according to a''''flanking berm'''' mode so as to counterbalance the said center highloading materials by the weight of embankment materials distributedoutward therefrom in a counterbalancing manner.
 3. An embankment roadconstructed of a prescribed particulate material on terrain comprising asurface layer of light compressible soil material of relatively highwater content, this road comprising: a substrate mat structure placedupon this terrain so as to define the contemplated road and support saidparticulate road material; and an array of said road particulatematerials distributed upon said mat structure so as to developsufficient static loading on said compressible soil material at thecenter of the roadway to thereby render it relatively rigid andincompressible under contemplated surface loading and thus form animproved highly stable roadway structure; said mat being formed tocomprise a continuous structural-integral layer of water-imperviousmaterials while supporting the described loads without rupture thereof.4. The road structure recited in claim 3 wherein said mat is comprisedof relatively rigid polymeric materials.
 5. The composition as recitedin claim 4 wherein said mat includes rigid stiffener means affixedthereon directly under the maximum-loaded traffic sections of the roadso as to minimize any ''''rolling wave'''' phenomenon.
 6. Thecombination as recited in claim 4 wherein said mat comprises a layer ofpolyurethane foam material of sufficiently high compressive strength tosupport the contemplated loading without rupture and a supplementalreinforcement layer.
 7. The combination as recited in claim 6 whereinsaid polyurethane foam is applied in a multi-laminate form and wherein aprecoat of water-impervious material is applied prior to application ofthe foam and said reinforcement layer is nylon mesh material.
 8. Thecombination as recited in claim 7 wherein said precoat is comprisedprimarily of bituminous materials extended by a polymeric extenderadapted for low temperature flexibility of the mat in service.
 9. Amethod of floating an improved more stable gravel road atop muskeg-typeterrain comprising the steps of: a. Placing a continuously structurallyintegral polymeric water-impervious mat upon the terrain surface so asto define the roadway site; b. Distributing particulate materials uponthis mat so as to form the roadway embankment in a manner that developsa central traffic-supporting region of maximum uniform weight, tendingto depress the portion of the supporting mat thereunder and consolidatethe supporting muskeg materials thereunder.
 10. The combination asrecited in claim 9 wherein the particulates are distributed in a''''flanking berm'''' mode so as to develop said depressed central matsection and maximum central static loading while also counterbalancingand stabilizing this and gradually diminishing the static loading upwardtherefrom thereby minimizing any sharp discontinuities of stress uponthe underlying mat and minimizing resultant shear and a tendency torupture.
 11. The combination as recited in claim 9 wherein rigidreinforcing stiffener means is affixed to the mat structure alongportions thereof underlying the contemplated traffic load, said meansbeing sufficiently rigid to minimize and ''''rolling wave''''phenomenon.
 12. The combination as recited in claim 9 wherein said matis so formed and comprised of materials as to render a monolithicstructure distributing loads over a larger area of supporting terrainand so as to function as a barrier, both to the intrusion of moistureand to the escape of particulate roadway materials therefrom.